Exemplary embodiments of the invention relate to a method for producing a rotationally symmetrical shaped article.
Such shaped articles are used in many different areas. The production of an axle journal or pivot pin shall be mentioned here by way of example, as disclosed for example in German patent document DE 10 2013 101 555 B3.
The production of the shaped article known therefrom and made of metal, especially steel, and which in addition to an integrally formed hub comprises a bell-shaped bottom part provided with contouring, preferably occurs by using a tube as a semi-finished product, wherein the formed hub is sealed at its outer end by deforming, so that the shaped article is present in its final configuration as a component which is open on one side.
Although the use of a circular blank is mentioned in the aforementioned literature as a semi-finished product, further details in this respect are not provided.
However, applications for such an axle journal or pivot pin are provided in which the hub needs to be provided with an inner toothing, for example, into which a corresponding part engages, which can be inserted from the outside. In this respect, the interior space of the shaped article shall only be open on the side opposite the hub but closed in all other respects to form a depot for grease, which is used for the operation of rolling bodies positioned in the interior space during operation of the shaped article.
To provide such an axle journal, which therefore comprises a bell-shaped bottom part that is open on one side and a hub that is open to the outside and adjoins the bottom part, the respective formation of the hub as well as the bottom part occurred until now by forging and subsequent machining of the hub to introduce an inner bore.
This type of production can only be conducted with great effort, leading to unacceptable production costs, which are especially deplorable since such shaped articles are used as serial products in large numbers.
Furthermore, the forging to form such a shaped article requires high material input, which on the one hand similarly has a negative effect on the production costs and on the other hand, especially in the case of pivot pins or axle journals used in motor vehicles, runs counter to the permanently demanded reduction and optimization concerning the weight.
The invention is therefore directed to a method of the generic kind in which production of the rotationally symmetrical shaped article is possible with optimization concerning the production and the material.
Exemplary embodiments of the invention provide a method for manufacturing a rotationally symmetrical shaped article, which is manufactured in a forming process and comprises a cylindrically shaped, concentric hub that is axially closed on one side, in which at least one rotatable spinning roller acts on a rotating, closed and preferably planar circular blank made from sheet metal, with which material, by reducing the thickness of the circular blank, is pressed radially from the outside inwardly against a projecting part that runs upright on the circular blank by forming the hub, especially by forming a blind hole within the hub. The spinning roller is moved inwardly radially from the outside, so that a hub is formed by a forming process.
As was noticed surprisingly, a rotationally symmetrical shaped article can be produced by generally known spin forming using a spinning roller by using a closed metallic circular blank in accordance with the invention, i.e., a circular blank without a central hole, which rotationally symmetrical shaped article can be further processed into differently configured end products. Because no central hole is present, a blind hole is advantageously and simply formed within the hub, which is advantageous when the region within the hub is formed in a closed manner, e.g., if a grease depot is to be formed.
The starting product for further processing is the rotationally symmetrical shaped article produced according to the method described above and which is present in the simplest configuration by consisting of a radially extending flange that is planar on both sides and an adjoining hub that is formed as a hollow cylinder with a closed base and is open towards the side facing away from the flange.
A machining process for producing said hub is thus no longer necessary, thus not only providing the aforementioned advantages with respect to production, but also such concerning the load-bearing capacity. This is especially advantageous as a result of the missing notch effect by the fiber orientation interrupted during forming within the terms of the invention.
It is provided according to a further aspect of the invention to provide the hub with an inner and/or outer toothing, wherein this also occurs without machining and preferably during the forming of the hub. For this purpose, the projecting part is provided with a respective profiling on the outside, whereas for forming an outer toothing a die is provided that acts on the exterior side on the formed hub and is also provided with a respective profiling. Apart from that, the projecting part is driven with the same rotational speed as the rotating circular blank.
As was surprisingly recognized, the formation of the hub is especially simple if the circular blank is heated to a temperature of approximately 400° C. to 1200° C. during the forming of the hub.
In a subsequent working step, the radial flange of the circular blank or the formed shaped article adjoining the hub can be formed into a bell-shaped bottom part, wherein an exemplary and preferred configuration is shown in the aforementioned German patent document DE 10 2013 101 555 B3. The base of the blind hole preferably lies between the hub and the bell-shaped bottom part.
The forming preferably also occurs after heating, preferably in a temperature range beneath a hardening temperature.
The shaping of the bell-shaped bottom part can occur by pressing by means of a suitable pressing die or by pressing by means of a rotating spinning roller in interaction with a contour mandrel.
In the case of machining of the shaped article into an axle journal or pivot pin, whose bell-shaped bottom part comprises cage or ball tracks, the bell-shaped bottom part that is present as a blank is preferably partially heated in the regions which during the subsequent forming are formed into cage tracks by pressing against the contour mandrel. The heating can preferably also occur to a temperature of between approximately 400° C. and 1200° C.
The stamping of the cage tracks occurs according to a further aspect of the invention by means of stamping beams that are moved linearly against each other and between which the shaped article is positioned as a blank of this method step on the contour mandrel, wherein the contour mandrel on the one hand and the stamping beams on the other hand are each provided with a profiling, which correspond to each other to such an extent that the contour of the cage track is formed.
In this process, the cage tracks can be hardened by press hardening simultaneously with the formation thereof, wherein it is a further advantage of this method step to already bring the cage tracks with respect to their dimensioning to a target dimension or with an oversize if hard machining is to occur subsequently.
The ball tracks which are necessary for the proper use of the pivot pin are also formed by means of the stamping beams and optionally post-hardened.